There is a need for devices to provide access to internal regions of a living body, such as the circulatory system or body cavities, in circumstances requiring, for example, repeated withdrawal of blood, peritoneal dialysis, or injections of drugs, which may be continuous or repeated. While access to the circulatory system is ordinarily gained by use of a needle and syringe, repeated injections may cause scarring and eventual collapse of the vein or infection. Therefore, when repeated injections or blood withdrawals are required, a percutaneous access device is implanted, through which access may be gained to the circulatory system and thereafter closed off.
A number of designs for blood access devices have been developed. Devices utilizing rubber septums have, in particular, been associated with numerous problems. The amount of pressure exerted upon the septum by the blood access device itself is critical for insuring that the device remains sealed. This requires precise machining of such devices, with exacting tolerances and the accompanying high cost. Further, the septums have been susceptible to tearing by the needles utilized to either inject or withdraw liquids through the device, necessitating the difficult operation of replacing the damaged septum. Problems have also developed with devices that use sliding or rotating valves to control access to the circulatory system because blood may seep into the valve mechanism, causing the valve to stick. Such sticking is especially troublesome because a surgically implanted device is not easily accessible for repairs. Furthermore, blood which has seeped into the valve mechanism is a breeding ground for bacteria which may cause infection in the patient, and stagnant blood or denatured protein in the valve mechanism can cause clotting.
All blood access devices are inconvenient and unsightly, and for cosmetic reasons, a blood access device should be as small as possible. However, it is desirable to obtain a fluid flow rate through the device sufficient to perform the required injection or withdrawal in the shortest possible time. Accordingly, the passageway communicating with the region exterior of the body should be designed to minimize the resistance to flow therethrough.
Additionally, a blood access device for permanent implantation in the human body must be biocompatible with body tissue to prevent rejection reactions and associated infection. Surfaces which interface with blood should be thromboresistant to prevent blood clotting.